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United States Patent |
6,100,764
|
Kim
|
August 8, 2000
|
Remote control preamp circuit
Abstract
A pre-amp circuit including a photodiode, first and second amplifiers and a
differential amplifier reduces or eliminates noise in an input signal. The
photodiode converts an external optical signal into an electrical signal
which includes noise. The first amplifier amplifies the difference between
an output voltage of the photodiode, including the noise, and the
reference voltage, to generate a difference signal which includes a first
noise component. The second amplifier buffers the reference voltage to
generate a signal which includes a second noise component which is
in-phase with the first noise component. The differential amplifier
amplifies the difference between the voltages output from the first and
second amplifiers to generate an output signal which is substantially
devoid of such noise. The present invention is amenable to application in
remote control receiver systems.
Inventors:
|
Kim; Byeong-Il (Bucheon, KR)
|
Assignee:
|
Samsung Electronics Co., Ltd. (KR)
|
Appl. No.:
|
224831 |
Filed:
|
January 4, 1999 |
Foreign Application Priority Data
Current U.S. Class: |
330/308; 250/214A; 330/301 |
Intern'l Class: |
H03F 003/08 |
Field of Search: |
330/308,301,59
359/189
250/214 A
|
References Cited
U.S. Patent Documents
4163950 | Aug., 1979 | Damm et al. | 330/252.
|
Foreign Patent Documents |
62-102610 | May., 1987 | JP | 330/308.
|
2-196504 | Aug., 1990 | JP | 330/308.
|
3-165609 | Jul., 1991 | JP | 330/308.
|
94-25145 | Sep., 1994 | KR.
| |
Primary Examiner: Pascal; Robert
Assistant Examiner: Choe; Henry
Attorney, Agent or Firm: Samuels, Gauthier & Stevens LLP
Claims
What is claimed is:
1. A pre-amp circuit for eliminating noise in an amplified output signal
generated from a received input signal including such noise comprising:
a photodiode for converting an externally generated optical signal into an
electrical signal, said electrical signal including a noise signal;
a first amplifier having an inverting input connected to the output of the
photodiode and having a non-inverting input to which a reference voltage
is applied, the non-inverting input being isolated from the photodiode,
for amplifying the difference between the voltage of the electrical signal
and the reference voltage, and for generating a difference signal which
includes a first noise component;
a second amplifier having a non-inverting input to which the reference
voltage is applied for buffering the reference voltage, said buffered
reference voltage including a second noise component substantially
in-phase with said first noise component; and
a differential amplifier, for generating an output signal by amplifying the
difference between the voltage of the difference signal and the buffered
reference voltage, thereby eliminating said noise from the output signal.
2. The pre-amp circuit as claimed in claim 1, wherein the
externally-generated optical signal is an infrared signal.
3. The pre-amp circuit as claimed in claim 1, wherein the first amplifier
further comprises a resistor connected between the inverting input of an
operational amplifier and the output of the operational amplifier.
4. The pre-amp circuit as claimed in claim 1, wherein the second amplifier
further comprises a resistor connected between the inverting input of an
operational amplifier and the output of the operational amplifier.
5. The pre-amp circuit as claimed in claim 1, wherein the differential
amplifier comprises:
a first transistor having control electrode connected to the output of the
first amplifier for receiving the difference signal;
a first resistor connected between a first electrode of the first
transistor and a power supply voltage, for applying a voltage lower than
the power supply voltage thereto;
a second transistor having a control electrode connected to the output of
the second amplifier for receiving the buffered reference signal;
a second resistor connected between a first electrode of the second
transistor and the power supply voltage, for applying a voltage lower than
the power supply voltage thereto;
a third transistor having a first electrode connected to the second
electrodes of both the first and second transistors and having a control
electrode connected to a control signal for activating the differential
amplifier; and
a third resistor connected between the second electrode of the third
transistor and a ground port, for raising the second electrode of the
third transistor to a predetermined voltage.
6. The pre-amp circuit as claimed in claim 5, wherein the first transistor
is an NPN transistor having a base connected to the output of the first
amplifier, a collector connected to the first resistor, and an emitter
connected to the second electrode of the second transistor.
7. The pre-amp circuit as claimed in claim 5, wherein the second transistor
is an NPN transistor having a base connected to the output of the second
amplifier, a collector connected to the second resistor, and an emitter
connected to the second electrode of the first transistor.
8. The pre-amp circuit as claimed in claim 5, wherein the third transistor
is an NPN transistor having a collector connected to the second electrodes
of the first transistor and the second transistor, a base connected to the
control signal, and an emitter connected to the third resistor.
9. The pre-amp circuit as claimed in claim 5, further comprising:
a fourth resistor connected between the second electrode of the first
transistor and the first electrode of the third transistor; and
a fifth resistor connected between the second electrode of the second
transistor and the first electrode of the third transistor, the fourth and
fifth resistors preventing overcurrent from flowing through the third
transistor.
10. A method for eliminating noise in an amplified output signal generated
from a received input signal including such noise comprising:
converting an externally-generated received optical input signal into an
electrical input signal, said electrical signal including a noise signal;
amplifying the difference between the voltage of the electrical input
signal and a reference voltage electrically isolated from the electrical
input signal at a first amplifier, thereby generating a difference signal
which includes a first noise component;
buffering the reference voltage at a second amplifier, said buffered
reference voltage including a second noise component substantially
in-phase with said first noise component; and
applying the difference signal and the buffered reference voltage to a
differential amplifier, thereby eliminating said noise from the output
signal.
11. A pre-amp circuit for eliminating noise in an amplified output signal
generated from a received input signal including such noise comprising:
a photodiode for converting an externally generated non-differential
optical signal into an electrical signal, said electrical signal including
a noise signal;
a first amplifier having an inverting input connected to the output of the
photodiode and having a non-inverting input to which a reference voltage
is applied, for amplifying the difference between the voltage of the
electrical signal and the reference voltage, and for generating a
difference signal which includes a first noise component;
a second amplifier having a non-inverting input to which the reference
voltage is applied for buffering the reference voltage, said buffered
reference voltage including a second noise component substantially
in-phase with said first noise component; and
a differential amplifier, for generating an output signal by amplifying the
difference between the voltage of the difference signal and the buffered
reference voltage, thereby eliminating said noise from the output signal.
12. The pre-amp circuit as claimed in claim 11, wherein the
externally-generated optical signal is an infrared signal.
13. The pre-amp circuit as claimed in claim 11, wherein the first amplifier
further comprises a resistor connected between the inverting input of an
operational amplifier and the output of the operational amplifier.
14. The pre-amp circuit as claimed in claim 11, wherein the second
amplifier further comprises a resistor connected between the inverting
input of an operational amplifier and the output of the operational
amplifier.
15. The pre-amp circuit as claimed in claim 11, wherein the differential
amplifier comprises:
a first transistor having control electrode connected to the output of the
first amplifier for receiving the difference signal;
a first resistor connected between a first electrode of the first
transistor and a power supply voltage, for applying a voltage lower than
the power supply voltage thereto;
a second transistor having a control electrode connected to the output of
the second amplifier for receiving the buffered reference signal;
a second resistor connected between a first electrode of the second
transistor and the power supply voltage, for applying a voltage lower than
the power supply voltage thereto;
a third transistor having a first electrode connected to the second
electrodes of both the first and second transistors and having a control
electrode connected to a control signal for activating the differential
amplifier; and
a third resistor connected between the second electrode of the third
transistor and a ground port, for raising the second electrode of the
third transistor to a predetermined voltage.
16. The pre-amp circuit as claimed in claim 15, wherein the first
transistor is an NPN transistor having a base connected to the output of
the first amplifier, a collector connected to the first resistor, and an
emitter connected to the second electrode of the second transistor.
17. The pre-amp circuit as claimed in claim 15, wherein the second
transistor is an NPN transistor having a base connected to the output of
the second amplifier, a collector connected to the second resistor, and an
emitter connected to the second electrode of the first transistor.
18. The pre-amp circuit as claimed in claim 15, wherein the third
transistor is an NPN transistor having a collector connected to the second
electrodes of the first transistor and the second transistor, a base
connected to the control signal, and an emitter connected to the third
resistor.
19. The pre-amp circuit as claimed in claim 15, further comprising:
a fourth resistor connected between the second electrode of the first
transistor and the first electrode of the third transistor; and
a fifth resistor connected between the second electrode of the second
transistor and the first electrode of the third transistor, the fourth and
fifth resistors preventing overcurrent from flowing through the third
transistor.
20. A method for eliminating noise in an amplified output signal generated
from a received input signal including such noise comprising:
converting an externally-generated received non-differential optical input
signal into an electrical input signal, said electrical signal including a
noise signal;
amplifying the difference between the voltage of the electrical input
signal and a reference voltage at a first amplifier, thereby generating a
difference signal which includes a first noise component;
buffering the reference voltage at a second amplifier, said buffered
reference voltage including a second noise component substantially
in-phase with said first noise component; and
applying the difference signal and the buffered reference voltage to a
differential amplifier, thereby eliminating said noise from the output
signal.
21. A pre-amp circuit for eliminating noise in an amplified output signal
generated from a received input signal including such noise comprising:
a photodiode for converting an externally generated optical signal into an
electrical signal, said electrical signal including a noise signal;
a first amplifier having an inverting input connected to the output of the
photodiode and having a non-inverting input to which a reference voltage
is applied, for amplifying the difference between the voltage of the
electrical signal and the reference voltage, and for generating a
difference signal which includes a first noise component;
a second amplifier having a non-inverting input to which the reference
voltage is applied for buffering the reference voltage, said buffered
reference voltage including a second noise component substantially
in-phase with said first noise component; and
a differential amplifier, for generating an output signal by amplifying the
difference between the voltage of the difference signal and the buffered
reference voltage, thereby eliminating said noise from the output signal;
wherein the differential amplifier comprises:
a first transistor having control electrode connected to the output of the
first amplifier for receiving the difference signal;
a first resistor connected between a first electrode of the first
transistor and a power supply voltage, for applying a voltage lower than
the power supply voltage thereto;
a second transistor having a control electrode connected to the output of
the second amplifier for receiving the buffered reference signal;
a second resistor connected between a first electrode of the second
transistor and the power supply voltage, for applying a voltage lower than
the power supply voltage thereto;
a third transistor having a first electrode connected to the second
electrodes of both the first and second transistors and having a control
electrode connected to a control signal for activating the differential
amplifier; and
a third resistor connected between the second electrode of the third
transistor and a ground port, for raising the second electrode of the
third transistor to a predetermined voltage.
22. The pre-amp circuit as claimed in claim 21, wherein the first
transistor is an NPN transistor having a base connected to the output of
the first amplifier, a collector connected to the first resistor, and an
emitter connected to the second electrode of the second transistor.
23. The pre-amp circuit as claimed in claim 21, wherein the second
transistor is an NPN transistor having a base connected to the output of
the second amplifier, a collector connected to the second resistor, and an
emitter connected to the second electrode of the first transistor.
24. The pre-amp circuit as claimed in claim 21, wherein the third
transistor is an NPN transistor having a collector connected to the second
electrodes of the first transistor and the second transistor, a base
connected to the control signal, and an emitter connected to the third
resistor.
25. The pre-amp circuit as claimed in claim 21, further comprising:
a fourth resistor connected between the second electrode of the first
transistor and the first electrode of the third transistor; and
a fifth resistor connected between the second electrode of the second
transistor and the first electrode of the third transistor, the fourth and
fifth resistors preventing overcurrent from flowing through the third
transistor.
Description
BACKGROUND OF THE INVENTION
In a remote control system, signals encoded as infrared rays are used to
remotely direct system functions. A remote control transmitter generates
control signals, and encodes them as infrared rays which are transmitted
to a remote control receiver. The receiver receives the infrared rays and
controls a system using the encoded signal information.
FIG. 1 is a circuit diagram of a conventional remote control preamp
circuit. The conventional preamp circuit 10 includes a photodiode 11, a
differential amplifier 21, resistors 31, 32 and 33 and a capacitor 41.
An anode of the photodiode 11 is grounded, and a cathode thereof is
connected to a non-inverting (+) input of the differential amplifier 21.
The photodiode 11 receives an infrared ray 12 from an external source and
converts the input infrared ray 12 into current which is supplied to the
non-inverting (+) input of the differential amplifier 21.
Resistor 31 is likewise connected to the non-inverting (+) input of the
differential amplifier 21. A reference voltage (Vref) is applied to the
non-inverting (+) input via resistor 31, together with the output of the
photodiode 11.
Resistor 32 provides a feedback path between the output Vo terminal and
inverting input (-) terminal of the differential amplifier 21. Resistor 32
is connected directly between the terminals, and resistor 33 and capacitor
41 are coupled in series between the inverting input (-) and ground GND.
External noise may enter the non-inverting (+) and inverting (-) inputs of
the differential amplifier 21. The difference between the voltages of the
noise applied to the non-inverting (+) and inverting (-) inputs is
amplified by the differential amplifier 21, and the amplified noise is
included in the output signal Vo. Thus, even where the input noise is
weak, powerful noise is generated as it is amplified by the differential
amplifier 21, which can cause a system, for example a remote control
system, to malfunction.
SUMMARY OF THE INVENTION
The present invention relates to a preamp circuit and method, and more
particularly, to a preamp circuit and method adaptable for use in a remote
control for mitigating the effects of external noise in a manner which
overcomes the limitations of conventional embodiments.
Accordingly, the apparatus of the present invention is directed to a
pre-amp circuit including a photodiode, first and second amplifiers, and a
differential amplifier.
The present invention includes a pre-amp circuit for eliminating noise in
an amplified output signal generated from a received input signal
including such noise. The circuit includes a photodiode, a first feedback
amplifier, a second feedback amplifier, and a differential amplifier. The
photodiode converts an externally-generated optical signal into an
electrical signal, the electrical signal including a noise signal. The
first feedback amplifier includes an inverting input connected to the
output of the photodiode and a non-inverting input to which a reference
voltage is applied for amplifying the difference between the voltage of
the electrical signal and the reference voltage, and for generating a
difference signal which includes a first noise component. The second
feedback amplifier includes a non-inverting input to which the reference
voltage is applied for buffering the reference voltage. The buffered
reference voltage includes a second noise component which is substantially
in-phase with the first noise component. The differential amplifier
generates an output signal by amplifying the difference between the
voltage of the difference signal and the buffered reference voltage,
thereby eliminating said noise from the output signal.
In a preferred embodiment, the externally-generated optical signal
comprises an infrared signal. The first and second feedback amplifiers
preferably further comprise a resistor connected between the inverting
input of the operational amplifier and the output of the operational
amplifier.
The differential amplifier preferably comprises a first transistor having a
control electrode which is connected to the output of the first amplifier
for receiving the difference signal. A first resistor is connected between
a first electrode of the first transistor and a power supply voltage for
applying a voltage lower than the power supply voltage thereto. A second
transistor has a control electrode connected to the output of the second
amplifier for receiving the buffered reference signal. A second resistor
is connected between a first electrode of the second transistor and the
power supply voltage, for a applying a voltage lower than the power supply
voltage thereto. A third transistor has a first electrode connected to the
second electrodes of both the first and second transistors and further
includes a control electrode connected to a control signal for activating
the differential amplifier. A third resistor is connected between the
second electrode of the third transistor at a ground port for raising the
second electrode of the third transistor to a predetermined voltage. The
transistors preferably comprise NPN transistors.
In a preferred embodiment, a fourth resistor is connected between the
second electrode of the first transistor and the first electrode of the
third transistor, and a fifth resistor is connected between the second
electrode of the second transistor and a first electrode of the third
transistor, the fourth and fifth resistors preventing overcurrent from
flowing through the third transistor.
In this manner, an output signal is generated which is substantially devoid
of said noise.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the invention
will be apparent from the more particular description of preferred
embodiments of the invention, as illustrated in the accompanying drawings
in which like reference characters refer to the same parts throughout the
different views. The drawings are not necessarily to scale, emphasis
instead being placed upon illustrating the principles of the invention.
FIG. 1 is a schematic circuit diagram of a conventional remote control
preamp circuit.
FIG. 2 is a schematic circuit diagram of a remote control preamp circuit
according to the present invention.
FIG. 3 illustrates waveforms of input and output signals when external
noise is applied to the inputs of the first and second amplifiers shown in
FIG. 2.
FIG. 4 is a flow diagram of a pre-amplification method in the pre-amp
circuit according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference to FIG. 2, a remote control pre-amp circuit according to a
preferred embodiment of the present invention comprises a photodiode 211,
first and second amplifiers 221, 231 and a differential amplifier 241.
The anode of the photodiode 211 is grounded and the cathode is connected to
an inverting (-) input of the first amplifier 221. The photodiode 211
converts an externally-generated optical signal, e.g., infrared rays, into
an electric signal.
The first amplifier 221 includes a first operational amplifier 223 and a
first feedback resistor 225. The output of the photodiode 211 is applied
to the inverting (-) input of the first operational amplifier 223, and a
reference voltage Vref is applied to the non-inverting (+) input of the
first operational amplifier 223. The first feedback resistor 225 is
connected between the inverting (-) input and the output of the
operational amplifier 223. The first amplifier 221 amplifies the
difference between the output voltage of the photodiode 211 and the
reference voltage Vref. An amplified voltage Vo1 is transferred to the
differential amplifier 241.
The second amplifier 231 includes a second operational amplifier 233 and a
second feedback resistor 235. The reference voltage Vref is applied to the
non-inverting (+) input of the second operational amplifier 233. The
second feedback resistor 235 is connected between the inverting (-) input
and the output of the second operational amplifier 233. The second
amplifier 231 serves to buffer the reference voltage Vref. A buffered
voltage Vo2 is transferred to the differential amplifier 241.
The differential amplifier 241 includes first, second, and third NPN
transistors Q1, Q2, Q3, and first through fifth resistors R1-R5.
A base, a collector and an emitter of the first NPN transistor Q1 are
connected to the output of the first amplifier 221, the first resistor R1
and the fourth resistor R4, respectively, as shown. When the voltage Vo1
of the output of the first amplifier 221 is greater than a voltage applied
to the emitter of the first NPN transistor Q1, by a predetermined voltage
(about 0.7V for a silicon transistor or about 0.3V for a germanium
transistor), the first NPN transistor Q1 becomes active.
A base, a collector and an emitter of the second NPN transistor Q2 are
connected to the output of the second amplifier 231, the second resistor
R2 and the fifth resistor R5, respectively, as shown. When the voltage Vo2
of the output of the second amplifier 231 is greater than a voltage
applied to the emitter of the second NPN transistor Q2, by a predetermined
voltage (about 0.7V for a silicon transistor or about 0.3V for a germanium
transistor), the second NPN transistor Q2 becomes active.
A base of the third NPN transistor Q3 is connected to a control signal P1,
a collector thereof is connected to both the fourth and fifth resistors R4
and R5, and an emitter thereof is grounded via the third resistor R3. When
the control signal P1 is greater than a voltage applied to the emitter of
the third NPN transistor Q3, by a predetermined voltage (about 0.7V for a
silicon transistor or about 0.3V for a germanium transistor), the third
NPN transistor Q3 is activated. Activation of the third NPN transistor Q3
in turn activates the differential amplifier 241.
The first resistor R1 is connected between a power supply voltage Vcc and
the collector of the first NPN transistor Q1, and the second resistor R2
is connected between the power supply voltage Vcc and the collector of the
second NPN transistor Q2. The first and second resistors R1 and R2 reduce
the power supply voltage Vcc, and the reduced power supply voltage is
applied to the collectors of the first and second NPN transistors Q1 and
Q2.
The third resistor R3 is connected between the emitter of the third NPN
transistor Q3 and the ground port (GND). A voltage drop occurs as current
flows from the emitter of the third NPN transistor Q3 to the ground port
(GND), raising the emitter of the third NPN transistor Q3 to a
predetermined voltage.
The fourth resistor R4 is connected between the emitter of the first NPN
transistor Q1 and the collector of the third NPN transistor Q3, and the
fifth resistor R5 is connected between the emitter of the second NPN
transistor Q2 and the collector of the third NPN transistor Q3. In the
fourth resistor R4, a voltage drop occurs as current flows from the
emitter of the first NPN transistor Q1, to prevent overcurrent from
flowing through the third NPN transistor Q3. In the fifth resistor R5, a
voltage drop occurs as current flows from the emitter of the second NPN
transistor Q2, to prevent overcurrent from flowing through the third NPN
transistor Q3.
The operation of the differential amplifier 241 will now be described.
Assuming the third NPN transistor Q3 is activated by signal P1, if voltage
Vo1, applied to the base of the first NPN transistor Q1, is greater than
voltage Vo2, applied to the base of the second NPN transistor Q2, then the
current flowing through the first NPN transistor Q1 is significantly
greater than the current flowing through the second NPN transistor Q2,
such that a voltage Vo3 at the collector of the first NPN transistor Q1 is
lowered to nearly a ground voltage. On the contrary, if voltage Vo1 is
smaller than voltage Vo2, then the current flowing through the first NPN
transistor Q1 is significantly smaller than the current flowing through
the second NPN transistor Q2, such that the voltage Vo3 at the collector
of the first NPN transistor Q1 is raised to nearly the power supply
voltage Vcc.
The voltage Vo4 at the collector of the second NPN transistor Q2 is
generally opposite the voltage Vo3 at the collector of the first NPN
transistor Q1. That is, when the voltage Vo3 approaches the power supply
voltage Vcc, the voltage Vo4 becomes nearly the ground voltage. When the
voltage Vo3 approaches the ground voltage, the voltage Vo4 of the
collector of the second NPN transistor Q2 becomes nearly the power supply
voltage Vcc.
FIG. 3 illustrates the behaviour of waveforms of input and output signals
when external noise is included in the input signals provided to the first
and second amplifiers 221 and 231 for voltages Vo1, Vo2, and Vo3. When
such noise is generated, the differential amplifier 241 operates to remove
all noise and amplifies only the signal output from the photodiode 211.
The operation of the pre-amp circuit shown in FIG. 2 will now be described
with reference to FIG. 3. When external noise 302 enters the input port of
the first amplifier 221, it is combined with the signal output 300 of the
photodiode 211, and the result is applied to the inverting (-) input of
the first amplifier 221. That is, the signal 300 applied to the input port
of the first amplifier 221 in effect has a distorted waveform. When noise
302 enters the input port of the first amplifier 221, noise having the
same phase also enters the input port of the second amplifier 231. The
phase of the noise at the output of the first amplifier 221 is therefore
the same as that of the noise at the output of the second amplifier 231.
The in-phase noise signals are applied to the first and second NPN
transistors Q1, Q2, which, as described above operate with opposite
collector voltages. This, in turn, causes a cancellation of the noise
signal in the differential amplifier 241 and thus, the differential
amplifier 241 amplifies only the signal output from the photodiode 211 and
generates an output signal Vo3, Vo4 which is substantially free of noise.
In a preferred embodiment, Vref comprises 2.5 volts; resistor 225 comprises
100K ohms; resistor 235 comprises 100K ohms; resistors R1, R2, R3, R4 and
R5 comprise 1K, 1K, 1K, 1K, and 2K ohms respectively; Q1 and Q2 comprise
NPN transistors; Vcc comprises 5 volts; and P1 comprise 1.0 volts. Other
resistance and voltage values may be employed, and are equally applicable,
depending on the type of operational amplifiers 233, 2335 and transistors
Q1, Q2, Q3 used, and depending on the application.
FIG. 4 is a flow diagram illustrating a pre-amplification method in the
pre-amp circuit according to the present invention. Referring to FIG. 4,
the pre-amplification method is comprised of an optical signal conversion
step 411, first and second amplifying steps 421 and 431, and a
differential amplifying step 441.
In step 411, the photodiode 211 receives an external optical signal and
converts the optical signal into an electrical signal. The optical signal
may comprise, for example an infrared signal.
In step 421, the electrical signal generated in step 411 is amplified along
with any accompanying noise in the first amplifier 221.
In step 431, the noise is likewise applied to a second amplifier 231.
In step 441, when the phase of the noise amplified in step 421 is the same
as that of the noise amplified in step 431, the noise is removed by the
differential amplifier 241, and only the electrical signal amplified in
step 421 is amplified and output.
While this invention has been particularly shown and described with
references to preferred embodiments thereof, it will be understood by
those skilled in the art that various changes in form and details may be
made therein without departing from the spirit and scope of the invention
as defined by the appended claims.
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